Method Of Electrolytic Deposition Of Arsenic From Industrial Electrolytes Including Waste Electrolytes Used In Electrorefining Of Copper After Prior Decopperisation Of Electrolyte

ABSTRACT

The subject of the present invention is a method of the electrolytic isolation of arsenic from industrial electrolytes including waste electrolytes used in the electrorafination of copper after its prior decopperisation.

The subject of the present invention is a novel method of the electrolytic isolation of arsenic from waste electrolytes from the electrorefining of copper, a method of preparing electrolyte by its decopperisation as well as a method of isolation of arsenic from copper industry electrolytes with their prior decopperisation.

The annual production of copper electrolytes produced by way of the electrorefining of copper in 2009 was over 15000000 tons worldwide. As it is demonstrated by the data of W. G. Davenport, M. King and M. Schlesinger, Extractive Metallurgy of Copper, Elsevier Science Ltd. Oxford, Great Britain, published in 2002 the electrolytic refinement produces copper of a very high purity, over 99.9% by mass of Cu. During copper production, one of the waste products is arsenic.

According to the publication by Andrzej Chmielarz, Copper Metallurgy, 50th Anniversary of KGHM Polska Miedź S A Kraków 2011. pp. 87 and 88, arsenic is a significant component of Polish copper concentrates. Annually, material processing is supplemented by about 2500 tons of arsenic. According to the same literature source, there are at least two material streams from which the reclamation and stabilization of arsenic are not fully mastered. One of these is the copper arsenide Cu₃As (the so-called copper arsenic sponge) which is formed during the decopperisation of post-refining electrolytes, whereas the second is a post-refining acid remaining after the decopperisation and crystallization of nickel sulphate. The arsenic content of these solutions is up to 20 g/l. According to other literature data, it is also known that during the currently used decopperisation methods, toxic gaseous arsenic, AsH₃, is emitted to the atmosphere.

The problem of isolating and stabilizing arsenic from solutions used in the copper industry in electrorefining is thus a significant technical, economic and ecological of the decopperisation industry. A second problem in need of a solution is the formation of the so-called copper-arsenic sponge during the electrolyte decopperisation for further dearsenification. Unexpectedly, the problems described have been solved by the present invention.

The first subject of the present invention is a method of electrolytic isolation of arsenic from a post-refining electrolyte characterised in that it is embodied using a single-stage potentiostatic arsenic isolation process, preferably on a steel cathode, in the cathode potential range of from −1.20 V to −1.70 V in relation to the anode, preferably of acid-resistant steel, wherein the electrolyte is not chemically processed. The isolation is conducted without any chemical processing of the electrolyte which, for contrast, is required in the solvent extraction (SX) as used at present in the isolation of copper salts from the post-refinement solution. Equally preferably, a method according to the present invention is characterised in that the electrodeposition is conducted at room temperature from 18° C. to 50° C., preferably from 18° C. to 30° C.

More preferably, a method according to the present invention is characterised in that the electrodeposition process makes use of an anode of a lead alloy, or based on titanium oxide and iridium wherein the cathode and anode surface areas are comparable.

The example anodes are already used in the galvanic industry in the electrodeposition of copper. More preferably a method according to the present invention is characterised in that the electrodeposition process is conducted using an anode of acid-resistant steel and then the anode surface area is at least 5-fold that of the cathode. Equally preferably, a method according to the present invention is characterised in that the electrodeposition is conducted using a cathode of acid-resistant steel or of copper. Most preferably, a method according to the present invention is characterised in that the process of electrodeposition is conducted with constant circulation of the electrolyte or with electrolyte mixing.

The second subject of the present invention is a method of decopperisation of a post-refining electrolyte, characterised in that it is embodied using a single-stage potentiostatic process isolation of copper on a cathode with a cathode potential range of from −1.00 V to −1.50 V in relation to the acid-resistant steel anode, wherein the electrolyte is not subjected to chemical processing. Equally preferably a method according to the present invention is characterised in that the electrodeposition process is conducted at room temperature from 18° C. to 50° C., preferably from 18° C. to 30° C. Equally preferably a method according to the present invention is characterised in that the electrodeposition process makes use of a lead alloy anode, or one based on titanium oxide and iridium, wherein the surface areas of the cathode and anode are comparable. More preferably, a method according to the present invention is characterised in that the electrodeposition process is conducted using an acid-resistant steel anode, wherein the anode surface area is at least 5-fold greater than the cathode surface area. W the next preferable embodiment of the present invention, the method is characterised in that the electrodeposition process is conducted using a cathode of acid-resistant steel or of copper. Also preferably, a method according to the present invention is characterised in that the electrodeposition process is conducted with constant electrolyte circulation or mixing.

The third subject of the present invention is a method of electrolytic isolation of arsenic from a post-refining electrolyte, characterised in that it encompasses

-   -   the preparation of a post-refining electrolyte according to a         method defined in the second subject of the present invention;     -   the isolation of arsenic according to a method defined in the         first subject of the present invention;

It turns out that after decopperisation according to the second subject of the present invention to a concentration of about 1 mg/ml it is possible to potentiostatically isolate arsenic with a purity greater than 99.5% on the cathode. The present invention relates to a method of electrolytic and potentistatic production of arsenic from electrolytes, in which the concentration of copper is about 1 mg/l.

The present invention has an advantage over the above described methods in that the proposed novel method of the electrolytic isolation of arsenic because it is based solely on a potentiostatic electrodeposition process in which:

-   -   a post-refining electrolyte is decopperised to a concentration         of about 1 mg/l, preferably according to the second subject of         the present invention;     -   after the decopperisation, preferably according to the second         subject of the present invention, the cathode is exchanged as         well as increasing the cathode potential by at least −200 mV         such that the isolation of arsenic proceeds at a commercially         effective rate,     -   during the potentistatic isolation of arsenic, the deposited         arsenic is such that it may be a commercial product, and not a         copper-arsenic sponge which is a troublesome waste product in         need of further processing,     -   the arsenic deposited during the above process is finally         removed from the material cycle and does not require further         processing or manipulation,     -   during the potentiostatic isolation of arsenic the toxic         arsenous gas AsH₃ is not produced.

In the method according to the present invention the process of decopperisation via the electrodeposition of copper from post-refining electrolytes is carried out using potentiostatic electrolysis: potentiostatic electrolysis with a cathode potential range of from −1.20 V to −1.70 V, in relation to an acid-resistant steel anode, wherein the time of electrolysis is dependent on an initial concentration of arsenic, the final concentration of arsenic that is to be achieved, the applied cathode potential, electrolyte mixing or flow rate as well as temperature. If the value of the resistance in Ohms IR is negligible, the range of cathode potentials in relation to the acid-resistant steel anode is from −1.20 V to −1.45 V. Due to the differing construction of the electrolysers, and the industrial electrolytes used (of varying conductivity and resistance), the potential drop entailed by the ohmic resistance can be from −0.2 to −0.5 V

-   -   the maximum value of the applied cathode potential is −1.70 V.

The present invention, defined in the second subject of the present invention, has an advantage over the above-defined methods in that the proposed decopperisation method is based solely on potentistatic electrodeposition, wherein:

-   -   the post-refining electrolyte is decopperised to a concentration         level of about 1 ppm (1 mg/dm³, thus the concentration of copper         in the decoppered solution is at least 200 times smaller than in         the presently used process) which has an economic, technical and         ecological significance;     -   the cathodic copper produced throughout the concentration range,         thus from about 50 g/dm³ to 1 mg/dm³ has a commercial purity,         meaning >99.9% by mass;     -   during the decopperisation an arsenous sponge is not produced;     -   during the decopperisation the toxic gas AsH₃ is not released.

EXAMPLE 1

In an electrochemical vessel thermoregulated to 25° C. there is an indicator electrode of steel plate with a surface area of about 2.5 cm2. which is the cathode, as well as a reference electrode (anode) in the form of a steel plate with a surface area of about 50 cm2 and a thickness of 0.15 cm. The vessel is filled with an industrial electrolyte after a presently used industrial decopperisation, and then according to the decopperisation method defined in the second subject of the present invention (example 3 and 4), therefore of the following composition: 0.001 g/dm³ Cu, 170 g/dm³ H₂SO₄ as well as 0.102 g/dm³ Fe, 0.147 g/dm³ Sb, 0.032 g/dm³ Co, 5.1 g/dm³ Ni, as well as 2.9 g/dm³ As. Using a BNC connector the electrodes are connected to a measurement device—a commercially available galvanostat/potentiostat which can be programmed to perform an electrolysis. During the electrolysis we measure current changes dependent on electrolysis duration. The size of the recorded current is connected to the changes in the concentration of arsenide ions in solution. The solution is not mixed.

The potentiostatic electrolysis parameters are: the potential of the steel cathode to the steel anode is E=−1.35 V and the electrolysis time is t=50 h.

After the electrochemical deposition of arsenic on an electrode, we evaluated the composition of the produced arsenic using EDS/EDX diffraction we determined that the resulting cathodic deposit of arsenic has a purity of >99.5% by mass.

EXAMPLE 2

In an electrochemical vessel thermoregulated to 25° C. there is an indicator electrode of steel plate with a surface area of about 2.5 cm2. which is the cathode, as well as a reference electrode (anode) in the form of a steel plate with a surface area of about 50 cm2 and a thickness of 0.15 cm. The vessel is filled with an industrial electrolyte after a presently used industrial decopperisation, and then according to the decopperisation method defined in the second subject of the present invention (example 3 and 4), therefore of the following composition: 0.001 g/dm³ Cu, 170 g/dm³ H₂SO₄ as well as 0.102 g/dm³ Fe, 0.147 g/dm³ Sb, 0.032 g/dm³ Co, 5.1 g/dm³ Ni, as well as 2.9 g/dm³ As.

Using a BNC connector the electrodes are connected to a measurement device—a commercially available galvanostat/potentiostat which can be programmed to perform an electrolysis. During the electrolysis we measure current changes dependent on electrolysis duration. The size of the recorded current is connected to the changes in the concentration of arsenide ions in solution. The solution is stirred at 50 RPM.

The potentiostatic electrolysis parameters are: the potential of the steel cathode to the steel anode is E=−1.350 V, and thus the potential is more cathodic by −200 mV than in the decopperisation process described in the second subject of the present invention, the electrolysis time is t=25 h.

After the electrochemical deposition of arsenic on an electrode, we evaluated the cathode deposit using EDS/EDX diffraction and we determined that the resulting cathodic deposit of arsenic has a purity of >99.5% by mass.

We also determined that the use of mixing with a greater cathode current density, and thus the rate of deposition of arsenic on the cathode. In example 2 the cathode current density grew by about 20 times in comparison to Example 1.

EXAMPLE 3

In an electrochemical vessel thermoregulated to 25° C. there is an indicator electrode of steel plate with a surface area of about 2.5 cm² which is the cathode, as well as a reference electrode (anode) in the form of a copper plate with a surface area of about 50 cm² and a thickness of 0.15 cm. The vessel is filled with an industrial electrolyte after an industrial decopperisation according to a presently used decopperisation method, meaning galvanostatic cascade deposition, with the following composition: 0.102 g/dm³ Cu, 170 g/dm³ H₂SO₄ as well as 0.102 g/dm³ Fe, 0.147 g/dm³ Sb, 0.032 g/dm³ Co, 5.1 g/dm³ Ni, as well as 2.9 g/dm³ As. Using a BNC connector the electrodes are connected to a measurement device—a commercially available galvanostat/potentiostat which can be programmed to perform an electrolysis. During the electrolysis we measured current changes dependent on the progress of the electrolysis. The size of the recorded current is connected to the changes in the concentration of copper ions in solution. The solution is mixed at a rate of 50 RPM.

The potentiostatic electrolysis parameters are:

the potential of the steel cathode to the steel anode is E=−1.150 V,

the electrolysis time is t=20 h

Following the electrochemical deposition of copper on an electrode, we evaluated the composition of the copper produced using X-ray diffraction and observed that the only contaminant in the produced cathode copper is oxygen in an amount of about 0.1% by mass. The resulting cathodic copper thus has a purity of >99.9% by mass. After electrolysis, the solution was analyzed using absorption atomic spectroscopy and we observed that the concentration of copper is 0.004 g/dm³ (4 ppm).

EXAMPLE 4

In an electrochemical vessel thermoregulated to 25° C. there is an indicator electrode of steel plate with a surface area of about 2.5 cm². which is the cathode, as well as a reference electrode (anode) in the form of a copper plate with a surface area of about 50 cm² and a thickness of 0.15 cm. The vessel is filled with an industrial electrolyte after an industrial decopperisation according to a presently used decopperisation method, meaning galvanostatic cascade deposition, with the following composition: 0.102 g/dm³ Cu, 170 g/dm³ H₂SO₄ as well as 0.102 g/dm³ Fe, 0.147 g/dm³ Sb, 0.032 g/dm³ Co, 5.1 g/dm³ Ni, as well as 2.9 g/dm³ As. Using a BNC connector the electrodes are connected to a measurement device—a commercially available galvanostat/potentiostat which can be programmed to perform an electrolysis. During the electrolysis we measured current changes dependent on the progress of the electrolysis. The size of the recorded current is connected to the changes in the concentration of copper ions in solution. The solution is not mixed.

The potentiostatic electrolysis parameters are: the potential of the steel cathode to the steel anode is E=−1.15 V and the electrolysis time is t=60 h

Following the electrochemical deposition of copper on an electrode, we evaluated the composition of the copper produced using X-ray diffraction and observed that the only contaminant in the produced cathode copper is oxygen in an amount of about 0.1% by mass.

The resulting cathode copper thus has a purity of >99.9% by mass. After electrolysis, the solution was analyzed using absorption atomic spectroscopy and observed that the concentration of copper is 0.002 g dm-3 (2 ppm).

EXAMPLE 5

From the decopperisation conducted as in example 3 or 4, we extracted the cathode and replaced it with a new one, meaning a steel plate with a surface area of about 2.5 cm2 and a thickness of 0.15 cm. Next, we performed dearsenification as in example 1 or 2. The potential of the steel cathode to the steel anode is

E=−1.350 V, and thus the potential is more cathodic by −200 mV than in the decopperisation process, the electrolysis time is t=25 h.

After the electrochemical deposition of arsenic on an electrode, we evaluated the cathode deposit using EDS/EDX diffraction and we determined that the resulting cathode deposition of arsenic has a purity of >99.5% by mass. We also determined that the use of mixing with a greater cathode current density, a thus the deposition rate of arsenic on the cathode. 

1. A method of electrolytic isolation of arsenic from a post-refining electrolyte, comprising a single-stage potentiostatic arsenic electrodeposition on a cathode having a potential range of from −1.20 V to −1.70 V in relation to the anode, wherein the electrolyte is not subjected to chemical processing.
 2. The method according to claim 1, characterised in that the electrodeposition process is conducted at room temperature from 18° C. to 50° C.
 3. A method according to claim 1, wherein the anode is a lead alloy anode, or a titanium oxide and iridium anode, and wherein the surface areas of the cathode and anode are comparable.
 4. The method according to claim 1, wherein the anode is an acid-resistant steel anode and the anode surface area is at least 5 times greater than the cathode surface area.
 5. The method according to claim 1, wherein the cathode is an acid-resistant steel or copper cathode.
 6. The method according to claim 1, characterised in that the electrodeposition process is conducted with constant electrolyte circulation or mixing.
 7. A method of decopperisation a post-refining electrolyte, comprising a single-stage potentiostatic copper electrodeposition on a cathode having a cathode potential range from −1.00 V to −1.50 V in relation to the acid resistant steel anode, wherein the electrolyte is not subjected to chemical processing.
 8. The method according to claim 7, characterised in that the electrodeposition process is conducted at room temperature from 18° C. to 50° C.
 9. A method according to claim 7, wherein the anode is a lead alloy anode, or a titanium oxide and iridium anode, and wherein the surface areas of the cathode and anode are comparable.
 10. The method according to claim 7, wherein the anode is an acid-resistant steel anode, and wherein the anode surface area is at least 5-fold greater than the cathode surface area.
 11. The method according to claim 7, wherein the cathode is an acid-resistant steel or copper cathode.
 12. The method according to claim 7, characterised in that the electrodeposition process is conducted with constant electrolyte circulation or mixing.
 13. A method of post-refining an electrolyte, characterised in that it encompasses: the preparation of a post-refining electrolyte according to a the method defined in claim 7; and the deposition of arsenic according to the method defined in claim
 1. 14. The method of claim 2, wherein the electrodeposition process is conducted at a temperature of 18° C. to 30° C.
 15. The method of claim 8, wherein the electrodeposition process is conducted at a temperature of 18° C. to 30° C. 